In her youth, Supersonic Sue was once a famous roller-derby queen until she was kicked out due to using enhanced rocket skates in her performances. Afterwards, she turned to a life of crime, becoming a role model for female villains. She also had a bitter rivalry with Baron Von Steamer, fighting over being Boss Awesome's number one enemy.
Role in the series
In her debut episode, Supersonic Sue engages in a bank robbery, which Hiro Hamada, Baymax and Go Go Tomago respond to. Despite outnumbering her, the more experienced villain out races them and escapes with Baymax's left rocket fist. She later uses the rocket fist to abduct Baron Von Steamer from prison, just as Big Hero 6 was visiting to question him on where to find her. She brings Steamer to his old ironworks lair, having fully set electrical systems, much to his consternation. Contrary to his assumption that she was planning on eliminating him to take the title of Boss Awesome's number one enemy, she proposed they join forces to defeat Boss Awesome once and for all. Steamer pridefully insisted he could accomplish that on his own before admitting he had yet to succeed. Sue suggested, "Don't get steamed, get even."
To that end, Steamer lures Big Hero 6 into a trap where the two villains overpower them and monologue about their plan to defeat Boss Awesome. Coincidentally, Boss Awesome came right to them, much to the villains' delight. Despite Sue pointing out that Boss Awesome had been out of the game for a while, Boss Awesome still leaped into action. Ultimately, Supersonic Sue overpowered Boss awesome with her "Flying Squirrel" technique and arrogantly proclaimed herself his true archenemy, causing Steamer to turn on her, and, in turn, he was defeated by Boss Awesome. As they were taken into custody, Sue admits to Go Go that she inspired her to put her skates back on. Steamer then asks Boss Awesome to settle whether he or Sue is his true archenemy. Boss Awesome declared his real archenemy to be cabbage soup, much to Steamer's anguish.